In general terms, an electric podded azimuth thruster is a marine propulsion unit consisting of a fixed pitch propeller mounted on a steerable gondola (“pod”) which also contains the electric motor driving the propeller. The podded azimuth thruster thus combines the action of a rudder, thruster and propeller into one revolving propulsion unit. In the podded azimuth thruster unit, the electric motor is mounted inside the propulsion unit and the propeller is connected directly to the motor shaft. By avoiding the use of a traditional propeller shaft, the propeller can be further below the stern of the ship in a clear flow of water, thereby providing greater hydrodynamic and mechanical efficiency. Furthermore, it increases flexibility in the general arrangement of the vessel's power plant. Electric power for the propulsion motor is conducted through slip rings that let the podded azimuth thruster unit rotate 360 degrees about the vertical axis. Because podded azimuth thruster units utilize fixed-pitch propellers, power is always fed through a variable-frequency drive or cycloconverter that allows speed and direction control of the propulsion motors.
From propulsion product availability performance point of view it is seen in history that shaft line bearings have the highest criticality importance factor of unscheduled dry-dockings. This means that in case of a ship needing to be dry docked due to propulsion product related damage, most likely the propulsion product related damage is caused by shaft line bearing failure. Thus, it is crucial to maintain operating context of bearings according to given maintenance instructions as well as to operate propulsion product based on given guidelines. In addition, predictive maintenance can be required to maximize likelihood to survive until the next scheduled dry docking, especially in case bearing damage occurred. Today this problem is solved using data from different sources, analyzed based mainly on expertise knowledge and recommendations by means of continuous as well as scheduled monitoring of bearing by several manual and automatic methods. Such monitoring can be cumbersome to perform and it could thus be difficult to accurately predict the remaining useful lifetime (RUL) of the podded azimuth thruster bearing.
Hence, there is still a need for an improved prediction of remaining useful lifetime of a bearing.